Vehicles generally include a cooling system that circulates a cooling fluid to regulate the temperature of various vehicle components. The cooling fluid is generally a water-based fluid that is mixed with a modifier, such as ethylene glycol to lower the freezing temperature and raise the boiling temperature. Although referred to as a cooling fluid, water, or coolant, the fluid may be used to heat or cool vehicle components or the vehicle cabin to a desired operating temperature. As used throughout this disclosure, references to coolant should be understood to include any type of cooling fluid used to raise or lower the operating temperature of one or more vehicle components. The coolant is generally circulated through a cooling circuit by one or more associated pumps. For vehicles having an internal combustion engine, including hybrid vehicles, a coolant or water pump may be mechanically operated by rotation of the engine crankshaft. Because of their reliance on engine operation, mechanically actuated coolant pumps operate only when the engine operates. A mechanically actuated water pump may be replaced by, or supplemented by, an electrically actuated water pump in various applications, such as hybrid vehicles. Similarly, electric vehicles that do not include an internal combustion engine may include a water pump to provide heating/cooling of various vehicle components, such as a traction battery and/or vehicle cabin. Electrically actuated water pumps provide greater control flexibility as they can be operated based on various vehicle and ambient operating conditions.
Vehicle cooling circuits may include various components to regulate the temperature of the coolant. For example, the cooling circuit may include a thermostat that limits or prevents coolant circulation through a heat exchanger or radiator to reduce the time needed for the coolant to attain a desired operating temperature. Coolant flow may also be directed through a heat exchanger or heater core in response to a request for cabin heating or battery conditioning, for example.
For applications that include an internal combustion engine and an electric water pump, the pump operation may be based on engine temperature and engine load, for example. While suitable for many applications, this can lead to more coolant flow than needed under some operating conditions.